Applied Mechanics and Materials Vols. 423-426

Abstract: Molecular dynamics simulations were performed to calculate the melting points of perfect crystalline aluminum to high pressures. Under ambientpressure, there exhibits about 20% superheating before melting compared to the experimental melting point. Under high pressures, thecalculated melting temperature increases with the pressure but at a decreasing rate, which agrees well with the Simon's melting equation. Porosity effect was also studied for aluminum crystals with various initial porosity at ambient pressure, which shows that the equilibrium melting point decreases with the initial porosity as experiments expect.

Abstract: Setellite21 cobalt-based alloy coating was deposited on 45 steel by electro-spark deposition. Microstructure and phase composition of the coating were analyzed. Wear resistance and wear mechanism of the coating were researched. The results indicate that the coating with compact structure is mainly composed of Co, Co₆W₆C, CoC_x and CoCr. Average microhardness of the coating is 445.34 HV_0.5, which is about 2 times to that of the substrate. The coating presents excellent wear resistance with no obvious peelings and scratches. Wear resistance of the coating is about 2.3~2.7 times to that of the substrate. Wear mechanism of the coating mainly contains abrasive wear and fatigue wear, and along with oxidization wear.

Abstract: This paper uses both numerical simulation method and experimental research method to study on welding residual stress of high-strength steel of the cone-cylinder hull. Welding is often accompanied by a larger welding residual stress, which directly affects the safety and service life of the hull structure. In order to obtain the distribution of the welding residual stress, the welding procedure was developed by its parameter language by using FE analysis software in this paper. Then the welding residual stress of hot spot region was measured through X-ray nondestructive testing method, and compared it with simulation results. Finally, considering the residual stress as the initial stress, this paper analyzed dynamic response process of the welding structure under combined actions of the welding residual stress and multiaxial loads, which could more accurately determine the stress of welding structure and the location of fatigue risk point. According to the amplitude of damage parameters and strain time-history curve, we can estimate the fatigue life of structure by selecting the corresponding damage models.

Abstract: Aims at the performance of the oil distribution plate parts with laser direct rapid forming, and referring to the role of ultrasonic vibration in areas such as casting, welding, sintering etc. , and utilizing the neural networks and the genetic algorithm to optimize the process parameters, the article does the basic research of laser direct rapid forming distribution plate parts based on the ultrasonic vibration. The results indicates that this study can greatly enhance the wear resistance, the corrosion resistance and the fatigue properties etc. of the laser sintering distribution plate parts, having a good guidance to the practical production.

Abstract: Crimping is widely used in production of large diameter submerged-arc welding pipes. Traditionally, the designers obtain the technical parameters for crimping from experience or trial-errors by experiments. However, it is difficult to obtain the ideal crimping technical parameters with this method immediately at present. To tackle this problem, a new method coupled with response surface methodology and finite element method is proposed to design crimping technical parameters and save the design time of crimping. In this paper, the crimping forming process is simulated by finite element (FE) code ABAQUS. Taking the crimping of X80 steel Φ1219mm×22mm×12000mm welding pipe for instance, the simulation data from the arrangement of simulation which is constituted by the optimal latin hyper-cube sampling approach is treated as sample point. Four types of response surface methodology which included four-order polynomial function, orthogonal polynomial function, kriging and radial basis function is discussed, where the response surface model based on radial basis function is proved more efficient than other types of response surface methodology to construct surrogate model. The results showed a good agreement by a comparison with simulation results and remarkably predicted the crimping quality. Thus, the presented method of this research provides an effective path to design crimping parameters.

Abstract: Nano cemented carbide is a new style cutter material. Because its grain size is very small, it is superior to common cemented carbide in properties, such as high hardness, fracture toughness, flexural strength and higher abrasion resistance. It is proposed to have wide application prospect to tools and mould manufacturing, machinery manufacturing, geological drilling, mining, oil field development, etc. In this paper, nanocemented carbide tool was ground with ELID technology, and the marble were cut with nanocemented carbide, and the cutting properties of nanocemented carbide were studied. Results imply that the tool life of nanocemented carbide is 0.5-1 times longer than that of common cemented carbide at low cutting speed. Which means the nanocemented carbide is more suitable for machining hard and brittle material than common cemented carbides at low cutting speed. And the microscopic analysis showed, the mechanism of tool wear is the abrasive wear as well as the shedding of WC hard phase within Co phase caused by the hard spots shed from the marble embedding in the internal part of binder phase Co which is located in the hard phase WC.

Abstract: A new forming method of honeycomb semi-cell structures was proposed by analyzing the defects of finished products processed by traditional roll forming method. Using ANSYS/LS-DYNA, a numerical analysis of its forming process was set up. A new forming equipment has been developed to conduct experiments. The results of experimental and numerical analysis show that the new forming method of the honeycomb semi-cell structures is feasible and superior.

Abstract: In order to solve the problem of low accuracy of honeycomb semi-cell structures which are rolled by traditional trapezoidal tooth profile gear shaping rollers, conjugate trapezoidal tooth profile gear shaping rollers have been put forward to improve the quality of honeycomb semi-cell structures, basing on the theoretical analysis. Using ANSYS/LS-DYNA, a finite element model of rolling aluminum foils by two kinds of tooth profile shaping rollers was set up. Then results of numerical simulation indicate that the honeycomb semi-cell structures rolled by the conjugate trapezoidal gear shaping rollers are closer to the ideal size than those rolled by the traditional trapezoidal gear shaping rollers.

Abstract: Springback is a common phenomenon in air bending of sheet metal forming, caused by the elastic redistribution of the internal stresses during unloading. It has been recognized that springback is essential for the design of the air bending. Traditionally, the values of springback is obtained for air bending parameters from handbook tables or springback graphs. However, the handbook tables or springback graphs are obtained using experiments and it is a time consuming processes. In this paper, a finite element model has been used to analyze the air bending process. Some experiments are carried out on ST12 materials, and the finite element model is validated comparing with experiments. In the present research the influence of process variables such as punch radius, die radius and die on springback are discussed using finite element analysis. Thus, the presented results of this research provide a basis of design to improve forming quality.

Abstract: Phosphorous slag and fly ash were used as raw materials for the preparation of ready-mixed mortar, and a series of technological parameters, such as phosphorus slag content, fly ash content, and chemical activators were investigated based on the compressive strength and setting time of specimens in this paper and the performances of products were also tested. The results showed that the optimal mix proportion for preparing ready-mixed mortar (M10) is as follows: cement 5%, phosphorous slag 10%, fly ash 10%, sand 75%, water reducer 1% and chemical activator 1%. The consistency, water retaining, setting time, 28d compressive strength, 14d bond strength and 28d shrinkage meet the requirement of Chinese standard GB/T 25181-2010.